1. Field of the Invention
This invention is in the field of data bus fault isolation couplers and methods therefor, and more particularly, is a coupler and method for a data bus fault isolation coupler featuring a coupling transformer with integrated resistance in a set of windings.
2. Description of the Related Art
Modern aircraft, ground and ocean platforms employ many on-board computer systems. These computer systems are concerned with command functions, platform control operations, and many other types of electronic system interfacing within or on the platform. In the military context, the installation and interconnection of the electronic systems with various computer systems is controlled by Military Specification requirements.
The Military Specifications for aircraft, spacecraft, ground vehicles and ocean vessels specify the linking of the various computer systems and electronic systems onboard with a Local Area Network type network built to military specifications. Typically, these interconnect systems onboard are called data bus networks. Within the United States military aircraft data bus networks are built to MIL-STD-1553B requirements, currently in revision B. Additionally, European military aircraft data bus networks are built to MIL-STD-1553B and STANAG 3838 requirements. The contents of MIL-STD-1553B and STANAG 3838 are incorporated herein by reference.
Both the United States and the European specifications specify that these data bus networks have electrical fault protection placed between the main data bus and each separate component, computer system, or terminal connected thereto. Specifically, each connection to the main data bus requires that a data bus coupler, constructed to the standards of MIL-STD-1553B and/or STANAG 3838 requirements be utilized between the main data bus and the component, computer system, or terminal connected to the main data bus. The MIL-STD-1553B and STANAG 3838 specifications require that directly coupled data bus couplers be built with internal fault isolation resistors to be placed in series with a step-up transformer to provide for protection to the main data bus in the event of a fault or short in a connected component or computer system. This interrelation of main data bus, data bus coupler, and component or computer system according to the prior art is shown in FIG. 1.
Presently, all data bus couplers are constructed using two wire non-inductive wound resistors connected in series with a coupling transformer. This configuration of components is usually packaged on a printed wring board (PWB), or potted into a Mil Spec MIL-T-21038 transformer module.
However, many drawbacks to this system and method of constructing data bus couplers exist. The addition of the two separate wire wound resisters increases the cost of the data bus coupler because not only the transformer must be purchased, but also the two wire wound resistors must be purchased, and all these components must meet the requirements of the applicable Military Specifications. Additionally, all the components must be electrically coupled together internal to the data bus coupler. This internal coupling of components effects the Mean Time Between Failures (MTBF). MTBF is an indicator of expected system reliability calculated on a statistical basis from the known failure rates of various components of the system, is usually expressed in hours, and may address both systems and individual population items. MTBF in a system is also directly proportional to the number of components and the number of electrical couplings, or joints, between each component. As the addition of the resistors adds two components and two joints, the MTBF will therefore be affected. Finally, the space required for the combination of the transformer and the two wire wound resistors is much greater than merely for a transformer alone.
Therefore a need existed for a system and method of removing the two separate wire wound resistors from a data bus coupler in order to reduce the cost, reduce the size of the coupler, and increase the MTBF of the coupler. Additionally, a need existed for a system and method of incorporating the required fault protection resistance into the transformer windings in order to meet the protection requirements of MIL-STD1553B.